The current state of the art in treating neurological disorders such as epilepsy or Parkinson's disease involves either drugs or the open-loop electrical stimulation of neurologic tissue. Drug therapy has been shown to have significant short and long term side effects and is often ineffective. In U.S. Pat. No. 3,850,161, Liss describes a continuous closed-loop feedback system which will always feedback part of the brain EEG signal to separate electrodes so that if a large EEG signal occurs it will be fed back in an attempt to cancel out the original signal. This system does not take advantage of recently developed digital signal processing and microcomputer technology by which feedback signals can be activated only when a neurological event occurs, nor does it provide a practical means to recognize and intervene during early stages in the evolution of a neurological event. In addition, the Liss device is not programmable and it does not provide a means to record EEG signals. Examples of a "neurological event" are the occurrence of an epileptic seizure or the occurrence of a migraine headache. A "neurological event" is defined herein as either the precursor of an event such as an epileptic seizure, or the epileptic seizure itself.
Maurer and Sorenson in U.S. Pat. No. 4,019,518 describe a combined internal/external system for electrical stimulation of the body with biphasic pulses but do not describe any means of detecting neurological events. Fischell in U.S. Pat. No. 4,373,527 describes a programmable medication infusion system but does not anticipate its use in response to a detected neurological event.
More recently, a device has been approved for human use to stimulate the vagus nerve in a continuous fashion with the objective of decreasing the rate of epileptic seizures. Clinical reports on such devices indicate only a modest degree of success in that only 50% of the patients experience a greater than 20% reduction in the rate of epileptic seizures. Another device that has been recently introduced into clinical practice utilizes continuous stimulation of the thalamus for the treatment of involuntary motion disorders such as Parkinson's syndrome.
Neither of these two open-loop devices described above is highly effective for the treatment of a neurological disorder such as epilepsy, and neither anticipates the use of decision making in order to optimize a response to turn off the neurological event nor the recording of EEG signals.
The automatic implantable cardiac defibrillator is an example of a decision making device having data recording capability that has been successfully used in a decision based closed-loop mode for the treatment of ventricular fibrillation. However, the requirements for detection and treatment of ventricular fibrillation are significantly simpler and certainly different from the requirements for a device to detect and treat an impending epileptic seizure. Specifically, an implantable cardiac defibrillator requires only a single signal, namely the heart's ECG, in order to detect a fibrillation event. What is more, only a single pair of electrodes is required for detection of the fibrillation event and that same pair of electrodes can be used to provide an electrical stimulus for electrical defibrillation. A heart defibrillator electrode is adapted to be placed on or in close proximity to the heart and is not suitable for use as a brain electrode.
Coker and Fischell in U.S. Pat. No. 4,581,758 describe sophisticated signal processing techniques using the sum of squared signals from two microphones to identify the direction with respect to a person from whom human speech originates. Although the Coker and Fischell patent teaches several signal processing techniques which may be applied with others to detect neurological events, the Coker and Fischell method is aimed at identifying the location of the speech source, while one of the goals of the present invention is to utilize the known location of the source of EEG signals to help identify an abnormal EEG which signifies an impending neurological event.
The NeuroCybernetic Prosthesis System recently made available for the treatment of epileptic seizures, utilizes continuous open-loop stimulation of the vagus nerve. This device does not sense the onset of an epileptic seizure, and it utilizes wires that are placed in the neck. Because of the frequent motions of such wires, they will have a tendency to fracture. No existing system utilizes electrodes, electrical wires and a control module that are entirely contained within the patient's scalp and essentially all contained within the patient's cranium. Such systems would not have any repeated bending of connecting wires thereby improving long term reliability. Furthermore, the NeuroCybernetic Prosthesis System does not use a rechargeable battery, nor does it utilize a separate external device controlled by the patient to activate the implanted system at the start of a neurological event in order to decrease the severity or time duration of the neurological event.